This invention relates to a method for making orthophosphorous acid and phosphine. More particularly, this invention is a method for the preparation of orthophosphorous acid and phosphine from elemental phosphorus and water. Still more particularly, this invention is a method for the preparation of orthophosphorus acid and phosphine by way of a hydroiodic acid-catalyzed reaction of elemental phosphorus with water.
Methods for making orthophosphorus acid, H.sub.3 PO.sub.3, have long been known. More recently, practical methods for preparing orthophosphorous acid have been developed, including a process whereby the trivalent oxide is formed by a controlled air oxidation of elemental phosphorous and subsequently hydrolyzed, as is disclosed in U.S. Pat. No. 3,528,772. Such processes produce a mixture of acids containing orthophosphorous acid together with as much as 25% orthophosphoric acid, H.sub.3 PO.sub.4, or more. Separating the orthophosphorous acid from the mixture in a highly purified form thus requires additional process steps such as those disclosed in U.S. Pat. Nos. 3,632,311 and 3,679,374.
Alternative prior art methods for obtaining orthophosphorous acid include the hydrolysis of a phosphorous trihalide such as phosphorus triiodide (PI.sub.3) with water to produce orthophosphorous acid and the corresponding hydrogen halide. An improved process employing this scheme is disclosed in U.S. Pat. No. 3,437,439, and includes the steps of in situ generation of PI.sub.3 from phosphorous and iodine in the presence of an oxidizing agent and a solvent, followed by hydrolysis to form orthophosphorous acid. As with the air oxidation processes previously discussed, this process forms a mixture containing a substantial proportion of orthophosphoric acid which must then be subjected to a separation process step if pure orthophosphorous acid is desired.